Certain portable battery-operated devices such as cellular telephones, personal digital assistants, cameras and media players, have multiple integrated functions. In addition to the functions that are directly involved in the nominal purpose of the unit, such as voice communications by a cellular telephone or recording image data by a digital camera, other functions of the device are supportive of the main function. Examples are battery chargers, status indication displays, audio annunciators, and the like. Still other functions are convenient combinations of diverse functions in one device. An example of a convenient combination is a cellular telephone capable of recording image data. The communications function of the device is useful to send the image data to another device for viewing or storage.
All of the functional elements and subassemblies comprise electrical loads on the power supply, typically comprising a battery. In different states of operation, particular loads might be active and sinking current or quiescent and drawing little or no current. Among these loads are devices and subassemblies such as application processors, battery chargers, camera modules, video processors, RF modems, network interface modules (e.g., Bluetooth), MP3 audio players and amplifiers, associated memories, input/output displays and switch interfaces, etc.
All of these functions are coupled directly or indirectly to the power supply, typically comprising one or more Lithium-Ion batteries. The different functional elements may require voltage regulation. Some functional elements require DC/DC converters and switched mode power supplies (SMPS) to boost the DC voltage level. Three or four different SMPS units may be provided in new cellular designs for driving diverse functions. As many as 27 different voltage outputs may be provided in 2.5G and 3G cellular devices. The current load on the battery regularly exceeds one amp in a Time Division Multiple Access (TDMA) system when actively operating in an RF communication mode. The various other supply voltages, many of which are regulated, service audio and RF digital transceiver functions and also accessory switch control, LED drivers, vibrator drivers, ringer drivers, and more. Any one or more of these functions can draw current in the range of 0.01 to 1 Amp.
Such units also typically include battery charging circuits. In that case, the battery becomes a current sink. Nevertheless, other functions remain subject to activation. The supply of regulated voltages and such current as demanded by the respective functions continues.
All told, the power supply of a multifunction portable device such as a cellular telephone might service 20 to 30 functions in which one or more of the functional subassemblies is active, and several may be active at once. In a worst case, the power supply (e.g., one 4.2V Lithium Ion battery cell) may need to provide as much as 2 to 3 Amps.
Some of the functions are served by switching elements, amplifiers and the like, provided on board one or a limited number of integrated circuits. These circuits typically include a digital processor and memory for operation as a controller. Some of the other functions are served as peripheral circuits under switched control of the processor.
With such a configuration involving a number of current loads, there is a possibility that from time to time some particular load may fail, or an operational state may be assumed wherein an inordinate current load is presented by one or more of the devices. However, the particular current level that should be considered inordinate for a given load or subset of loads may differ between different operational states of the device. It would be advantageous to provide a power management arrangement that is programmed or contains sufficient conditional logic that it can appropriately identify problems that may arise in various operational scenarios, and can act to ameliorate problems, perhaps by making power distribution changes under its control, or decoupling one or more selected loads (possibly including a defective load), or automatically triggering a change to a different operational state of the device.
A power supply management scheme could prevent loss of communications or keep the battery from discharging more quickly than necessary or otherwise allocate the available power supply capacity to high priority uses. The available power would then provide service to certain priority functions and to retract support for other functions that may be malfunctioning or are considered low priority under the circumstances. With the increasing number of additional functions being served in the latest multifunction portable devices, the possibility and complication of these problems present challenges.
Simple switching schemes for limiting damage in the event of component failure along a current supply path are known. These schemes include thermal threshold shutdown devices, current fold-back limiting, rectifiers, fuses and so forth. Current limiting circuits contained in voltage regulators can be arranged to switch the regulator current output off, or into a low-current-output condition, when current drawn by a load exceeds some instantaneous or time-integrated threshold. Such circuits also can be made to emit a signal or to activate an indicator in the event of such a fault. However, reliance on internal current limiters in voltage regulators is not an optimal solution in a device having multiple loads and varying operational states. For example, a current fault threshold for a current limiting regulator is generally set at the very highest level of current that might be drawn in any operational state, and shuts down the output when the level is exceeded. Such a regulator provides protection against self damage, but It would be advantageous to have a more adaptive way to react to conditions, perhaps monitoring current loading conditions for a group of loads and using different current fault thresholds for respective loads in different operational states. What is needed is a sophisticated way to detect and to respond appropriately to current loading conditions involving a plurality of loads and operational conditions. By sensitivity to varying conditions, loads and regulators can be protected and the device also can appropriately allocate available power to loads that are considered priority loads in the particular operational state of the device at the time.
Even if an offending load is readily identifiable, it would also be advantageous to react with due consideration for the nature of the load and not necessarily simply to disable the offending load while continuing to serve other loads. Loads may be related, and there may be no point in providing current to a load that depends on operation of some other load once the other load has been turned off. For example, it is not useful to disable a transceiver function in a cellular telephone, even in adverse low battery or high current draw circumstances, while continuing to serve the audio or digital data processing functions that collect or process information fed to or from the transceiver. Loads may have priorities, and it may be desirable to attempt to maintain ongoing operations at the expense of less important features. For example, it may be desirable to maintain communications over audio playback or image capture capabilities, even if it is the communications circuits that appear to be faulty or marginal.
In order for a portable device to be capable of power management, the power distribution arrangements need to be configured to permit separate monitoring and separate control of loads, and potentially also to distinguish between internal and external loads. Such configurations and the control of the configuration to appropriately allocate power in a multifunction device, are novel aspects of the present invention. A power distribution control is integrated with due regard to the complexity of a cellular telephone or similar device, so as to react appropriately to a current fault, to discriminate among more and less critical functions, and where possible to allow the cellular device to continue functioning. The invention mitigates the impact of a failure of non-critical functions on the critical functions of the device, and provides for appropriate allocation of power supply capacity. Furthermore, the invention comprises a diagnostic tool that is useful for troubleshooting, repair, and signaling or indicating the state of operational conditions to the user.